Method and apparatus for preamble creation and communication in a wireless communication network

ABSTRACT

A wireless communications network uses a beamforming process to increase signal quality as well as transmission capabilities and reduction of interference. An improved Golay sequence is also used in the wireless communications network. In one aspect, the processes can be used to communicate regardless of whether the system is on an OFDM mode or a single carrier mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application Ser. No. 60/985,957, filed Nov. 6, 2007,entitled “OFDM preambles for beamforming and data packets.”

BACKGROUND

I. Field of the Disclosure

This disclosure relates generally to wireless communication systems and,more particularly, to wireless data transmission in a wirelesscommunication system.

II. Description of the Related Art

In one aspect of the related art, devices with a physical (PHY) layersupporting either single carrier or Orthogonal Frequency DivisionMultiplexing (OFDM) modulation modes may be used for millimeter wavecommunications, such as in a network adhering to the details asspecified by the Institute of Electrical and Electronic Engineers (IEEE)in its 802.15.3c standard. In this example, the PHY layer may beconfigured for millimeter wave communications in the spectrum of 57gigahertz (GHz) to 66 GHz and specifically, depending on the region, thePHY layer may be configured for communication in the range of 57 GHz to64 GHz in the United States and 59 GHz to 66 GHz in Japan.

To allow interoperability between devices or networks that supporteither OFDM or single-carrier modes, both modes further support a commonmode. Specifically, the common mode is a single-carrier base-rate modeemployed by both OFDM and single-carrier transceivers to facilitateco-existence and interoperability between different devices anddifferent networks. The common mode may be employed to provide beacons,transmit control and command information, and used as a base rate fordata packets.

A single-carrier transceiver in an 802.15.3c network typically employsat least one code generator to provide spreading of the form firstintroduced by Marcel J. E. Golay (referred to as Golay codes), to someor all fields of a transmitted data frame and to performmatched-filtering of a received Golay-coded signal. Complementary Golaycodes are sets of finite sequences of equal length such that a number ofpairs of identical elements with any given separation in one sequence isequal to the number of pairs of unlike elements having the sameseparation in the other sequences. S. Z. Budisin, “Efficient PulseCompressor for Golay Complementary Sequences,” Electronic Letters, 27,no. 3, pp. 219-220, Jan. 31, 1991, which is hereby incorporated byreference, shows a transmitter for generating Golay complementary codesas well as a Golay matched filter.

For low-power devices, it is advantageous for the common mode to employa Continuous Phase Modulated (CPM) signal having a constant envelope sothat power amplifiers can be operated at maximum output power withoutaffecting the spectrum of the filtered signal. Gaussian Minimum ShiftKeying (GMSK) is a form of continuous phase modulation having compactspectral occupancy by choosing a suitable bandwidth time product (BT)parameter in a Gaussian filter. The constant envelope makes GMSKcompatible with nonlinear power amplifier operation without theconcomitant spectral regrowth associated with non-constant envelopesignals.

Various techniques may be implemented to produce GMSK pulse shapes. Forexample, π/2-binary phase shift key (BPSK) modulation (orπ/2-differential BPSK) with a linearized GMSK pulse may be implemented,such as shown in I. Lakkis, J. Su, & S. Kato, “A Simple Coherent GMSKDemodulator”, IEEE Personal, Indoor and Mobile Radio Communications(PIMRC) 2001, which is incorporated by reference herein, for the commonmode.

SUMMARY

Aspects disclosed herein may be advantageous to systems employingmillimeter-wave wireless personal area networks (WPANs) such as definedby the IEEE802.15.3c protocol. However, the disclosure is not intendedto be limited to such systems, as other applications may benefit fromsimilar advantages.

According to an aspect of the disclosure, a method of communication isprovided. More specifically, the method includes obtaining an extendedGolay code selected from a set of extended Golay codes; modifying theextended Golay code; generating a preamble using the modified extendedGolay code; and transmitting the preamble.

According to another aspect of the disclosure, a communicationsapparatus is provided. The communication apparatus includes means forobtaining an extended Golay code selected from a set of extended Golaycodes; means for modifying the extended Golay code; means for generatinga preamble using the modified extended Golay code; and means fortransmitting the preamble.

According to another aspect of the disclosure, an apparatus forcommunications is provided. The communications apparatus includes aprocessing system configured to obtain an extended Golay code selectedfrom a set of extended Golay codes; modify the extended Golay code;generate a preamble using the modified extended Golay code; and transmitthe preamble.

According to another aspect of the disclosure, a computer-programproduct for wireless communications is provided. The computer-programproduct includes a machine-readable medium encoded with instructionsexecutable to obtain an extended Golay code selected from a set ofextended Golay codes; modify the extended Golay code; generate apreamble using the modified extended Golay code; and transmit thepreamble.

According to another aspect of the disclosure, a piconet coordinator isprovided. The piconet coordinator includes an antenna; and a processingsystem configured to obtain an extended Golay code selected from a setof extended Golay codes; modify the extended Golay code; generate apreamble using the modified extended Golay code; and transmit thepreamble via the antenna.

According to another aspect of the disclosure, a method of communicationis provided. More specifically, the method includes transmitting aplurality of quasi-omni packets from a first device, each quasi-omnipacket being transmitted in a particular quasi-omni pattern; and,transmitting a plurality of preambles from the first device, eachpreamble being transmitted in one of a plurality of directionalpatterns.

According to another aspect of the disclosure, a communicationsapparatus is provided, the communication apparatus includes means fortransmitting a plurality of quasi-omni packets from a first device, eachquasi-omni packet being transmitted in a particular quasi-omni pattern;and means for transmitting a plurality of preambles from the firstdevice, each preamble being transmitted in one of a plurality ofdirectional patterns.

According to another aspect of the disclosure, an apparatus forcommunications is provided. The communications apparatus includes aprocessing system configured to transmit a plurality of quasi-omnipackets from a first device, each quasi-omni packet being transmitted ina particular quasi-omni pattern; and transmit a plurality of preamblesfrom the first device, each preamble being transmitted in one of aplurality of directional patterns.

According to another aspect of the disclosure, a computer-programproduct for wireless communications is provided. The computer-programproduct includes a machine-readable medium encoded with instructionsexecutable to transmit a plurality of quasi-omni packets from a firstdevice, each quasi-omni packet being transmitted in a particularquasi-omni pattern; and transmit a plurality of preambles from the firstdevice, each preamble being transmitted in one of a plurality ofdirectional patterns.

According to another aspect of the disclosure, a piconet coordinator isprovided. The piconet coordinator includes an antenna; and a processingsystem configured to transmit a plurality of quasi-omni packets from afirst device, each quasi-omni packet being transmitted in a particularquasi-omni pattern; and transmit a plurality of preambles from the firstdevice, each preamble being transmitted in one of a plurality ofdirectional patterns.

According to another aspect of the disclosure, a method of communicationis provided. More specifically, the method includes detecting at leastone quasi-omni packet of a plurality of quasi-omni packets transmittedin a plurality of quasi-omni patterns from a first device; detecting apreamble transmitted in a directional pattern from the first device;determining a preferred pattern including at least one of a quasi-omnipattern and a directional pattern; and transmitting a feedback includingthe preferred pattern to the first device.

According to another aspect of the disclosure, a communication apparatusis provided. The communication apparatus includes means for detecting atleast one quasi-omni packet of a plurality of quasi-omni packetstransmitted in a plurality of quasi-omni patterns from a first device;means for detecting a preamble transmitted in a directional pattern fromthe first device; means for determining a preferred pattern including atleast one of a quasi-omni pattern and a directional pattern; and meansfor transmitting a feedback including the preferred pattern to the firstdevice.

According to another aspect of the disclosure, an apparatus forcommunications is provided. The communications apparatus includes aprocessing system configured to detect at least one quasi-omni packet ofa plurality of quasi-omni packets transmitted in a plurality ofquasi-omni patterns from a first device; detect a preamble transmittedin a directional pattern from the first device; determine a preferredpattern including at least one of a quasi-omni pattern and a directionalpattern; and transmit a feedback including the preferred pattern to thefirst device.

According to another aspect of the disclosure, a computer-programproduct for wireless communications is provided. The computer-programproduct includes a machine-readable medium encoded with instructionsexecutable to detect at least one quasi-omni packet of a plurality ofquasi-omni packets transmitted in a plurality of quasi-omni patternsfrom a first device; detect a preamble transmitted in a directionalpattern from the first device; determine a preferred pattern includingat least one of a quasi-omni pattern and a directional pattern; andtransmit a feedback including the preferred pattern to the first device.

According to another aspect of the disclosure, a communications deviceis provided. The communications device includes an antenna; and aprocessing system configured to detect at least one quasi-omni packet ofa plurality of quasi-omni packets transmitted in a plurality ofquasi-omni patterns from a first device; detect a preamble transmittedin a directional pattern from the first device; determine a preferredpattern including at least one of a quasi-omni pattern and a directionalpattern; and transmit a feedback including the preferred pattern to thefirst device.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Whereas some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following Detailed Description. The detaileddescription and drawings are merely illustrative of the disclosurerather than limiting, the scope of the disclosure being defined by theappended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects according to the disclosure are understood with reference to thefollowing figures.

FIG. 1 is a representation of a preamble for an OFDM communicationsignal in accordance with an aspect of the disclosure;

FIGS. 2A and 2B are flow charts for generating a modified Golay sequencefrom a regular Golay sequence in accordance with various aspect of thedisclosure;

FIGS. 3A and 3B is a plot of a time-domain filter configured inaccordance with one aspect of the disclosure and the resulting spectrumplot for a modified Golay sequence;

FIG. 4 is a structure diagram of a preamble having various lengths inaccordance with various aspect of the disclosure;

FIG. 5 is a block diagram of a Golay-code circuitry configured inaccordance with one aspect of the disclosure;

FIG. 6 is a structure diagram of a superframe structure for use inproactive beamforming as configured in accordance with one aspect of thedisclosure;

FIG. 7 is a structure diagram of a plurality of beacon structures to beused in a respective plurality of superframe structures similar to thesuperframe structure of FIG. 6;

FIGS. 8A and 8B are beamforming and superframe information elementsconfigured in accordance with one aspect of the disclosure;

FIGS. 9A and 9B are flow charts of a device with an omnidirectionalreceive antenna and a single directional antenna device, respectively,configured in accordance with various aspects of the disclosure;

FIGS. 10A, 10B, 10C and 10D are flow charts of a beamforming acquisitionprocess for a device configured in accordance with an aspect of theinvention;

FIGS. 11A and 11B relate to a process for on-demand beamformingconfigured in accordance with an aspect of the disclosure;

FIGS. 12A and 12B relate to a Q-omni information element transmittedfrom a first device to a second device as part of a Q-omni frametransmission and the feedback information element transmitted from thesecond device back to the first device;

FIGS. 13A to 13C illustrate a directional phase of on-demand beamformingconfigured in accordance with an aspect of the disclosure;

FIG. 14 is a diagram of a wireless network configured in accordance withan aspect of the disclosure.

FIG. 15 is a block diagram of a preamble generation apparatus configuredin accordance with an aspect of the disclosure;

FIG. 16 is a block diagram of a quasi-omni packet and directionalpreamble transmitter apparatus configured in accordance with an aspectof the disclosure;

FIG. 17 is a block diagram of a beamforming feedback apparatusconfigured in accordance with an aspect of the disclosure.

In accordance with common practice the various features illustrated inthe drawings may be simplified for clarity. Thus, the drawings may notdepict all of the components of a given apparatus (e.g., device) ormethod. In addition, like reference numerals may be used to denote likefeatures throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein are merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein.

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the disclosure. It should be understood, however, thatthe particular aspects shown and described herein are not intended tolimit the disclosure to any particular form, but rather, the disclosureis to cover all modifications, equivalents, and alternatives fallingwithin the scope of the disclosure as defined by the claims.

In one aspect of the disclosure, a dual-mode millimeter wave systememploying single-carrier modulation and OFDM is provided with asingle-carrier common signaling. The OFDM sampling frequency is 2592MHz, and OFDM transceivers in this aspect are configured to perform afast Fourier transform (FFT) of size 512, where only 352 of the 512subcarriers are used, yielding a bandwidth of 1782 MHz. Of the usedsubcarriers, 336 subcarriers are data-bearing and 16 subcarriers arepilots.

FIG. 1 is a representation of a preamble structure 100 for an OFDMcommunication signal in accordance with an aspect of the disclosure. Thepreamble structure 100 includes a packet sync sequence field 110, astart frame delimiter (SFD) field 140, and a channel-estimation sequence(CES) field 180. For an OFDM symbol of length N, the Kronecker (kron)product of a cover sequence of length L with a modified Golay sequenceof length M=N/L is used as a base sequence v of length N:

v=kron(c,u),

where c is the cover sequence of length L, and u is the modified Golaysequence of length M. One set of cover sequences is a subset of thefollowing sequences of length L:

IFFT([0 0 . . . 0 1 0 . . . 0]),

where IFFT is an inverse fast Fourier transform operation, and thesequence in parentheses has only one nonzero element. The position ofthe nonzero element may be varied to obtain different sets of coversequences. In accordance with various aspects of the disclosure, each ofa plurality of piconets is configured to use one or more of the basesequences for its preamble.

In one aspect of the disclosure, for an FFT size of 512 (i.e., M=512)and a modified Golay sequence of length 128 (i.e., M=128), the followinglength-4 cover codes (i.e., L=4) are used:

c(1)=IFFT([1 0 0 0])=[1 1 1 1];

c(2)=IFFT([0 1 0 0])=[1 j −1 −j];

c(3)=IFFT([0 0 1 0])=[1 −1 1 −1]; and

c(4)=IFFT([0 0 0 1])=[1 −j −1 j].

A first piconet controller (PNC) uses Golay sequence a1 with cover codec1 to form a first base sequence:

v1=[+a1 +a1 +a1 +a1] of length 512.

A second PNC uses Golay sequence a2 with cover code c2 to form a secondbase sequence:

v2=[+a2 +j.a2 −a2 −ja2] of length 512.

A third PNC uses Golay sequence a3 with cover code c3 to form a thirdbase sequence:

v3=[+a3 −a3 +a3 −a3] of length 512.

A fourth PNC uses Golay sequence a4 with cover code c4 to form a fourthbase sequence:

v4=[+a4 −j.a4 −a4 +ja4] of length 512.

The FFTs of the four base sequences, v1, v2, v3, and v4 are orthogonalto each other, as they occupy different OFDM subcarrier bins in thefrequency domain. For example, v1 occupies bins 0, 4, 8, . . . , v2occupies bins 1, 5, 9, . . . , v3 occupies bins 2, 6, 10, . . . , and v4occupies bins 3, 7, 11, . . . . This helps mitigate interference betweenthe preambles of the four piconets, and helps provide for improvedfrequency reuse and spatial reuse.

In one aspect of the disclosure, a regular Golay sequence (e.g., a1) isused to form a modified Golay sequence, b1. Although b1 occupies only128 sub-carrier bins (i.e., subcarriers 0,4,8 . . . ), the totalbandwidth comprises the entire 2592 MHz channel bandwidth since there isno guard band. The subcarriers corresponding to the size-512 FFT may benumbered from −256 to 255, which correspond to a bandwidth of 2592 MHz.Sub-carriers −176 to 176 denote to the useful bandwidth employed for thedata and pilots, whereas the subcarriers outside the range of −176 to176 may be used as guard bands.

FIG. 2A illustrates a modified Golay sequence generation process 200 forgenerating a modified Golay sequence u from a regular Golay sequence ain accordance with one aspect of the disclosure. In step 202, an FFTshift operation is provided to produce vector S, where:

S=fftshift(fft([a a a a]))

is a length-512 vector, and the operator fftshift centers the FFT (i.e.,it maps a sequence [0:511] to a centered sequence [−256:255]. In step204, subcarrier values of S outside a predetermined bandwidth are set tozero. For example, the subcarriers outside the range [−176:176] may beattenuated or zeroed. In an optional step 206, the amplitude of S withinthe range [−176:176] may be normalized. In step 208, real values of theIFFT of S are used to form a length-512 vector s:

s=real(ifft(S)).

In step 210, a modified Golay sequence u is generated from the first 128samples of s:

u=s(1:128).

FIG. 2B illustrates a second modified Golay sequence generation process250 for generating a second modified Golay sequence u in accordance withan aspect of the disclosure. In this approach, the generation of amodified Golay sequence is based on the modified Golay sequence being acyclic convolution between a regular Golay sequence and a shorttime-domain filter g. The time-domain filter g is configured to limitthe bandwidth of the resulting sequence to the actual bandwidth used fordata transmission.

In step 252, a time domain filter g of length L_(g) that has a bandwidthequal to a selected bandwidth, which in one example is a bandwidth of1782 MHz, is provided. An example of the time domain filter g isrepresented by a plot 300 in FIG. 3A. The 3-dB bandwidth of the channelbandwidth is one of many design parameters for determining the usedbandwidth, and consequently for yielding any of various filters. In step254, the modified Golay sequence u is generated from a cyclicconvolution of g and a regular Golay code a. In step 256, the resultingmulti-level, non-binary sequence may be transmitted or stored. Aspectrum plot 350 of the modified Golay sequence u is shown in FIG. 3B.

Receivers configured in accordance with method and apparatus aspects ofthe disclosure may provide for matched filtering relative to filter g.In one aspect, a receiver may include a filter matched to g, followed bya filter matched to the regular Golay code. Receivers employed inaccordance with aspects of the disclosure may be provided with aparallel receiving architecture.

In one aspect of the disclosure, subcarriers of each base sequence areinterleaved in frequency, and thus each base sequence occupies a quarterof the used channel bandwidth. In the absence of time and frequencysynchronization, however, interference may occur between piconetsemploying interleaved subcarriers. For example, a subcarrier 4 belongingto a PNC 1 may have adjacent subcarriers 3 and 5 belonging to a PNC 4and a PNC 2, respectively. In the absence of time and/or frequencysynchronization, the subcarriers 3 and 5 may leak into subcarrier 4,resulting in interference.

In one approach of addressing the interference caused by leakage,different cover sequences may be employed. For example, four coversequences, each of length 8, may be provided as follows:

C1=ifft([1 0 0 0 0 0 0 0])=[+1 +1 +1 +1 +1 +1 +1 +1],

C2=ifft([0 0 1 0 0 0 0 0])=[+1 +j −1 −j +1 +j −1 −j],

C3=ifft([0 0 0 0 1 0 0 0])=[+1 −1 +1 −1 +1 −1 +1 −1], and

C4=ifft([0 0 0 0 0 0 1 0])=[+1 −j −1 +j +1 −j −1 +j].

These cover sequences may be combined with a modified Golay sequence oflength 64 to generate four base sequences of length 512, wherein eachone occupies only ⅛^(th) of the used frequency band. Thus, each activesubcarrier is surrounded by 2 inactive (or null) subcarriers, thusreducing the interference. Alternative aspects of the disclosure may beconfigured for different cover-sequence lengths.

Referring again to FIG. 1, the Channel Estimation Sequence (CES) 180includes a pair of complementary modified Golay sequences va 182-1 andvb 182-2 produced from two length-512 complementary Golay sequences aand b. Each of the pair of modified Golay sequences va 182-1 and vb182-2 are preceded by a Cyclic Prefix (CP) 184-1 and CP 184-2,respectively. No cover sequences are used to generated the pair ofmodified Golay sequences va 182-1 and vb 182-2. The pair of modifiedGolay sequences va 182-1 and vb 182-2 are complementary, which allowsfor perfect channel estimation in either the time domain or thefrequency domain. In an alternative approach, two length-128complementary Golay sequences a and b, and two length-4 cover sequencesmay be used to generate the pair of length-512 complementary modifiedGolay sequences va 182-1 and vb 182-2. The modified Golay sequences va182-1 and vb 182-2 are complementary over length 128, thus stillallowing for perfect channel time estimation in either time or frequencydomains. In the time domain, channel estimation is provided over alength 128 Golay sequence. In the frequency domain, because only aquarter of the subcarriers are populated; channel estimation willrequire the use of interpolation.

In one aspect, the CES 180 may be repeated periodically to facilitatechannel tracking. In this case, the CES 180 is referred to as a pilotCES (PCES). Three periods are provided, and they correspond to rates of1, 3, and 6 ms.

FIG. 4 illustrates a preamble 400 in accordance with aspects of thedisclosure. Three preambles are defined as follows:

-   -   Long preamble: 8 sync symbols, 1 SFD symbol, 2 CES symbols    -   Medium preamble: 4 sync symbols, 1 SFD symbol, 2 CES symbols    -   Short preamble: 2 sync symbols, 1 SFD symbol, 1 CES symbol

During the beacon period, beacons with quasi-omni patterns, i.e.patterns that cover a broad area of the region of space of interest,referred to as “Q-omni” beacons, are first transmitted. Directionalbeacons—that is, beacons transmitted using some antenna gain in somedirection(s) may additionally be transmitted during the beacon period orin the CTAP between two devices.

A unique preamble sequence set may be assigned to each piconet withinthe same frequency channel, such as to improve frequency and spatialreuse. In one aspect of the disclosure, four preamble sequence sets(labeled by parameter m) are provided for frequency/spatial reuse. Apreamble sequence set comprises a length-512 base sequence s_(512,m) andtwo length-512 CES sequences u_(512,m) and v_(512,m). The base sequences_(512,m) is the Kronecker product of a length-4 cover sequence, c_(4,m)and a length-128 modified Golay sequence u_(128,m):

s _(512,m) [n]=c _(4,m)[floor(n/128)]×u _(128,m) [n mod 128]n=0:511

The base sequences s_(512,m) occupy four non-overlapping frequency-binsets, and therefore, are orthogonal in both time and frequency. Them^(th) base sequence occupies frequency bins m, m+4, m+8, m+12, . . . .In one aspect of the disclosure, modified Golay sequences are generatedfrom other Golay sequences, such as regular Golay complementarysequences, using time- or frequency-domain filtering to ensure that onlythe used subcarriers are populated rather than the entire 512subcarriers.

The term “regular Golay complementary sequences,” as used herein, anddenoted by a and b, may be generated using the following parameters:

1. A delay vector D of length M with distinct elements from the set 2 mwith m=0:M−1; and2. A seed vector W of length M with elements from the QPSK constellation(±1, ±j).

FIG. 5 illustrates a Golay-code circuitry 500 that may be employedeither as a Golay code generator or a matched filter in some aspects ofthe disclosure. The Golay-code circuitry 500 includes a sequence ofdelay elements 502-1 to 502-M configured for providing a determined setof fixed delays D=[D(0), D(1), . . . , D(M−1)] to a first input signal.The delay profile provided by the delay elements 502-1 to 502-M may befixed, even when the Golay-code circuitry 500 is configured to producemultiple Golay complementary code pairs. The Golay-code circuitry 500also includes a sequence of adaptable seed vector insertion elements530-1 to 530-M configured for multiplying a second input signal by atleast one of a plurality of different seed vectors W^(i)=[W(0), W(1), .. . , W(M−1)] to generate a plurality of seed signals. The output fromeach of the sequence of adaptable seed vector insertion elements 530-1to 530-M is fed into a first set of combiners 510-1 to 510-M to becombined with a respective output of each of the delay elements 502-1 to502-M. In the implementation of the Golay-code circuitry 500 as shown inFIG. 5, the output of each seed vector insertion element 530-1 to 530-Mis added to the output of its respective delay elements 502-1 to 502-Mby a respective one of the first set of combiners 510-1 to 510-M beforethe results then being fed to the next stage. A second set of combiners520-1 to 520-M is configured for combining the delayed signals from thedelay elements 502-1 to 502-M with signals multiplied by the seedvector, where the seed signals are subtracted from the delay signals inthe Golay-code circuitry 500.

Receivers implemented in accordance with certain aspects of thedisclosure may employ similar Golay-code generators to perform matchedfiltering of received signals so as to provide for such functionality aspacket or frame detection.

In one aspect, Golay codes (a1, a2, a3, and a4) may be generated bycombinations of Delay vectors (D1, D2, D3, and D3) and correspondingseed vectors (W1, W2, W3, and W4), as shown in the following table:

Delay and Seed Vectors for Golay a or b sequences a1, a2, a3 & a4 0 D164 32 8 1 4 2 16 0 D2 64 32 8 1 4 2 16 1 D3 64 32 4 2 8 1 16 0 D4 64 324 2 8 1 16 W1 −1 −j −1 −j −1 1 1 W2 −1 −1 1 +j 1 −j 1 W3 −1 −1 −1 −1 1+j 1 W4 −1 −1 1 −1 1 −j 1

The first, second, and fourth sequences are type a, whereas the thirdsequence is type b. Preferred sequences are optimized to have minimumsidelobe levels as well as minimum cross-correlation.

In some aspects of the disclosure, a base rate may be employed for OFDMsignaling operations used for exchanging control frames and commandframes, associating to a piconet, beamforming, and other controlfunctions. The base rate is employed for achieving optimal range. In oneaspect, 336 data subcarriers per symbol may be employed withfrequency-domain spreading to achieve the base data rate. The 336subcarriers (subcarriers −176 to 176) may be divided into 4non-overlapping frequency bins, such as described with respect to thepreamble, and each set may assigned to one of a plurality of PNCsoperating in the same frequency band. For example, a first PNC may beallocated subcarriers −176, −172, −168, . . . , 176. A second PNC may beallocated subcarriers −175, −171, −167, . . . , 173, and so on.Furthermore, each PNC may be configured for scrambling the data todistribute it over multiple subcarriers.

In IEEE 802.15.3, piconet timing is based on a super frame including abeacon period during which a PNC transmits beacon frames, a ContentionAccess Period (CAP) based on the CSMA/CA protocol, and a Channel TimeAllocation Period (CTAP), which is used for Management (MCTA) andregular CTAs, as further explained below

During the beacon period, beacons with almost omnidirectional antennapatterns, referred to as quasi-omni, or “Q-omni” beacons, are firsttransmitted. Directional beacons—that is, beacons transmitted using someantenna gain in some direction(s) may additionally be transmitted duringthe beacon period or in the CTAP between two devices.

In order to reduce overhead when transmitting directional beacons, thepreamble may be shortened (e.g., the number of repetitions may bereduced) for higher antenna gains. For example, when an antenna gain of0-3 dB is provided, the beacons are transmitted using a default preamblecomprising eight modified Golay codes of length 512 and two CES symbols.For an antenna gain of 3-6 dB, the beacons employ a shortened preambleof four repetitions of same modified Golay code and two CES symbols. Foran antenna gain of 6-9 dB, the beacons transmit a shortened preamble oftwo repetitions of the same modified Golay code and 1 or 2 CES symbols.For antenna gains of 9 dB or more, the beacon preamble employs only onerepetition of the same Golay code and 1 CES symbol. If a header/beaconis used during beaconing or for data packets, the header-data spreadingfactor may be matched to the antenna gain.

Various aspects of the disclosure provide for a unified messagingprotocol that supports a wide range of antenna configurations,beamforming operations, and usage models. For example, antennaconfigurations may include omnidirectional or quasi-omni antennas,directional antenna patterns of a single antenna, diversity-switchedantennas, sectored antennas, beamforming antennas, as well as otherantenna configurations. Beamforming operations may include proactivebeamforming, which is performed between a PNC and a device, andon-demand beamforming, which is performed between two devices. Differentusage models for both proactive beamforming and on-demand beamforminginclude per-packet beamforming from a PNC to multiple devices and fromat least one device to the PNC, transmissions from a PNC to only onedevice, communications between devices, as well as other usage models.Proactive beamforming is useful when the PNC is the data source formultiple devices, and the PNC is configured for transmitting packets indifferent physical directions, each of which corresponding to a locationof one or more devices for which packets are destined.

In some aspects, the unified (SC/OFDM) messaging protocol is independentof the beamforming algorithm and antenna configuration used in thedevices in wireless network 1400. This allows for flexibility in theactual beamforming algorithms employed. However, the tools enabling thebeamforming should be defined. These tools should support all scenarioswhile enabling reduced latency, reduced overhead, and fast beamforming.

The following table shows four types of single-carrier beamformingpackets that may be employed by aspects of the disclosure.

Preamble Requirement Length Header Rate Data Rate (M)andatory/ PacketType (# 128 chips) (Mbps) (Mbps) (O)ptional I 36 50 50 M II 20 100 100 OIII 12 200 200 O IV 8 400 400 O

Since these are single-carrier packets transmitted using the commonmode, they can be decoded by both single-carrier and OFDM devices. Themajority of transmitted packets may have no body—just a preamble.

The different types of packets may be employed for different antennagains in such a way as to substantially equalize the total gain of thetransmissions, taking into consideration both coding gain and antennagain. For example, a Q-Omni transmission with 0˜3 dB antenna gain mayemploy type I packets. A directional transmission with 3˜6 dB antennagain may use type II packets. A directional transmission with 6˜9 dBantenna gain may use type III packets, and a directional transmissionwith 9˜12 dB antenna gain may uses type IV packets.

FIG. 6 illustrates a superframe structure 600 that may be employed byvarious aspects of the disclosure to perform proactive beamforming. Themultipath channel environment between the PNC and a device is assumed tobe reciprocal, i.e. the channel from the PNC to the device is the sameas the channel from the device to the PNC. The superframe structure 600includes a beacon portion 650, a Contention Access Period (CAP) 660based on the CSMA/CA protocol, and Channel Time Allocation Period (CTAP)680, which is used for Management (MCTA) and regular CTAs. The beaconportion 650 includes a Q-omni section and a directional section. TheQ-omni section includes L transmissions in the superframe structure 600,which is a plurality of Q-Omni beacons, as represented by Q-Omni beacons610-1 to 610-L, each of which is separated by a respective MIFS (MinimumInterFrame Spacing which is a guard time), as represented by a pluralityof MIFS 620-1 to 620-L.

The CAP 660 is divided into a plurality of sub-CAPs (S-CAPs), which isrepresented by S-CAPs 662-1 to 662-L, each followed by a respectiveGuard Time (GT), which is represented by GTs 664-1 to 664-L. Thedirectional section 630-1 to 630-x contains a plurality of directionalpreambles.

In FIG. 7, the first L transmissions in a superframe structure 700,similar to the superframe structure 600 of FIG. 6, use Q-Omni beaconsthat, together, provide an omnidirectional pattern of beacontransmission. For a PNC capable of omnidirectional coverage—that is, aPNC having an omnidirectional-type antenna, L=1. For a PNC withsectorized antennas, L would represent the number of sectors that thePNC is able to support. Similarly, when a PNC is provided with switchingtransmit diversity antennas, L would represent the number of transmitantennas in the PNC.

Further, in the aspect of the disclosure shown in FIG. 7, the PNC isconfigured to beamform in J=N×M directions. Specifically, the PNC isable to send directional beacons in a determined number of directions aspart of the beamforming process. In one aspect, each directional beaconconsists only of a preamble and no header nor data. These directionalbeacons are referred to as directional preambles. The PNC is able tosend directional preambles in J directions, as represented bydirectional preambles 730-1-1 to 730-1-N for superframe beacon #1 702-1through directional preambles 730-M-1 to 730-M-N for superframe beacon#M 702-M, wherein a direction may include one or more beams. Thedirectional preamble are distributed over M superframes, as illustratedby superframes 702-1 to 702-M, with N directional preamble persuperframe, and the structure is periodic with a period of Msuperframes.

The CAP is divided into L sub-CAP periods corresponding to the L Q-Omnibeacons. During the l^(th) S-CAP, the PNC antenna transmits in the samedirection it used to transmit the l^(th) Q-Omni beacon. This caseassumes that the channel is reciprocal.

The first L beacons may be of any packet type. In one aspect,omnidirectional beacons use type I packets with a long preamble; Q-Omnibeacons sent with sectored antennas or antenna arrays with 3-6 dB gainuse type I or type II packets; and Q-Omni beacons using sectoredantennas or antenna arrays with 6-9 dB gain may use type I, type II, ortype III packets. In one aspect, the packet type used is communicated toother devices in the SFD. Thus, upon a successful detection of the SFD,a device will have knowledge of the header and data rates for thesubsequent portion of the packet and can use that knowledge tosuccessfully decode the packet.

Each Q-Omni beacon may carry a beamforming information element 840, suchas shown in FIG. 8A to convey the structure of the beamforming beaconsto all devices listening to the PNC. Once a device decodes any one ofthe Q-omni beacons during any superframe, it is capable of understandingthe entire beamforming cycle. In one aspect, the beamforming informationelement 840 includes a directional packet type field 842 (e.g., type I,II, III or IV), a current directional beacon identifier (ID) field 844,a number of superframes per beamforming cycle (e.g., the value M fromthe frame structure 700 of FIG. 7) field 846, a number of directionalpreambles per superframe (e.g., the value N from the frame structure 700of FIG. 7) field 848, a current Q-omni beacon ID field 850, a number ofQ-omni beacons (e.g., the value L from the frame structure 700 of FIG.7) field 852, a length field 854 containing the number of octets in theinformation element, and an element ID field 856, which is theidentifier of the information element. The current Q-omni beacon IDfield 850 contains a number identifying the number/position of thecurrent Q-omni beacon being transmitted in the current superframe withrespect to the number of Q-omni beacons field 852 in the superframe. Adevice, using the number contained in the current Q-omni beacon ID field850, will know which Q-omni direction from which it heard the beacon.

FIG. 8B illustrates a superframe information element 860 that istransmitted with the beamforming information element 840, and includes aPNC address field 862, a PNC response field 864, a piconet mode 866, amaximum transmission power level 868, a S-CAP duration field 870, anumber of S-CAP periods field 872, a CAP end time field 874, asuperframe duration field 876, and a time token 878.

FIGS. 9A and 9B illustrate two approaches for a beamforming operation bydevices in accordance with various aspect of the disclosure. FIG. 9A isdirected to a beamforming process 900 of a device with omnidirectionalreceive capabilities. In step 902 the omnidirectional device only needto detect the Q-omni beacons of one superframe. If the device is notomnidirectional, the device needs to sweep over all its receiveddirections by listening to one superframe for each receive direction forexample in order to detect the beacon. Upon detection of the Q-omnibeacons, the device stores a Link-Quality Factor (LQF) in step 904 foreach of the Q-omni beacons. Then, in step 906, the device sorts the LLQFs, [LQF(1), . . . , LQF(L)], and identifies the best PNC direction 1corresponding to the highest LQF:

1=arg{max[LQF(i)]}

i=1:L

In step 908, the device associates itself with the PNC during the l^(th)CAP of the current superframe, and instep 910 informs the PNC that allfurther communications should occur with the PNC using its l^(th) Q-omnidirection. The device may still track the set of L best directions bymonitoring the corresponding S-omni beacons every Q superframes. If adirection (e.g., the r^(th) S-omni direction) is found with a betterLQF, the device may inform the PNC to transmit the next packet using ther^(th) S-omni direction by encoding it in the “NEXT DIRECTION” field inthe PHY header.

FIG. 9B illustrates a beamforming process 920 performed by a device witha single directional antenna in accordance with an aspect of thedisclosure. In step 922, the device may receive an entire cycle of Msuperframes and when the device detects one of the Q-Omni beacons, itwill learn that it is receiving the m^(th) superframe, and will listento superframes m, m+1, . . . , m+M−1.

During the cycle of M superframes, the device measures, stores, andsorts J LQFs in step 924 corresponding to the J directional PNCdirections. During the same cycle, the device measures the L LQFscorresponding to the L S-omni PNC directions in step 926. Then, in step928, the device determines the best directional direction, j, and thebest Q-omni direction, 1. The device associates with the PNC during thel^(th) CAP of the (m+M−1)^(th) superframe and informs the PNC in step930 that all further communications should occur with the PNC using itsj^(th) directional direction. Optionally, the device may continue totrack the set of J directions by monitoring the correspondingdirectional beacons every Q×M superframes. If a direction r is foundwith a better LQF, the device may direct the PNC to update itsdirectional beam pattern to the device by encoding direction r in the“NEXT DIRECTION” field in the PHY header.

FIG. 10A illustrates an overview of a beamforming process 1000 inaccordance with an aspect of the disclosure that may be performed with adirectional device capable of transmitting and receiving in at least oneQ-omni direction and I directional directions. In step 1010, the devicewill perform Q-omni beacon detection. Once a beacon has been detected,the device will perform detection for directional preambles and the LQFstherefor in step 1020. In step 1030, the device can optionally rescanfor a preferred set of directional preambles. The rescan will allow thedevice to verify that the selected Q-omni directions are preferred.Lastly, in step 1040, the device will associate itself with the PNCbased on the preferred LQF.

FIG. 10B details the beacon detection process 1010 where, starting withstep 1010-1, the device sets a timeout and begins to search for a beaconin one of Q-omni directions. The device will search for a Q-omni beaconas long as the time has not expired in step 1010-2. If the detection issuccessful, as determined in step 1010-3, then the device will read thebeacon information and obtain all timing parameters of the Q-omnitransmission as well as the superframe. If the device starts listeningduring the m^(th) superframe, then upon detection of a Q-omni beacon(e.g., Q-omni beacon number 1), it discovers that it is listening duringthe m^(th) superframe. The device can set its directional pattern to thedirection of the beacon. If the device does not detect a Q-omni beacon,then operation continues with step 1010-4, where the device can startits own piconet or, in the alternative, go to sleep mode.

FIG. 10C details the directional preamble acquisition and LQFdetermination process 1020 where, in one aspect, as detailed in steps1020-1 to 1020-5, the device may listen to I×J superframes, Jsuperframes for each of its I directions as follows. The device sets itsdirectional direction to number 1, listens to M superframes (m, m+1, . .. , m+M−1), as shown in steps 1020-2, 1020-3 and 1020-1 and stores thecorresponding J LQFs, LQF(1,1) . . . LQF(1,J), wherein the first indexrefers to the device's direction, whereas the second index refers to thePNC's direction. In step 1020-3, the device sets its directionaldirection to number 2, listens to the next superframe, and stores the JLQFs: LQF(2,1) . . . LQF(2,J) in step 1020-1. These step are repeated adetermined number of (e.g., M) times. Upon the last iteration, thedevice sets its directional direction to number 1, listens to the next Msuperframes, and stores the J LQFs: LQF(I,1) . . . LQF(I,J).

FIG. 10D details the best directional determination process 1030, where,in step 1030-1, the device finds the best directional combination (i,j)referring to the device using its i^(th) directional direction and thePNC using it j^(th) directional direction. sorts the corresponding JLQFs, LQF(1,1) . . . LQF(1,J), In step 1030-2, the device can alsolisten to another I×M superframes for verification of the bestdirectional direction.

FIG. 10E details the device association process 1040 with the PNC where,in step 1040-1, the device sets its directional pattern to #1 and resetsthe superframe counter to zero. Then, in steps 1040-2 to 1040-5, thedevice will attempt to associate with the base station and pass the PNCthe preferred direction information. In one aspect, the device sends theinformation to the PNC during the l^(th) S-CAP period and informs thePNC of the best direction at this time. If the association is successfulin step 1040-4, then operation continues to step 10-6, where the devicedeclares a successful acquisition and switches its directional patternto the best direction.

In another aspect of the disclosure, the device can also perform aniterative process set its directional direction to number 1 and listensto the N directional beacons during the current superframe. If adirection j corresponding to the PNC's directional direction having anadequate LQF is found, then the device will associate to the PNC duringthe l^(th) S-CAP period and inform the PNC to use its j^(th) directionfor data communication. The device may still choose to scan for betterdirections, and if one is found, it informs the PNC to switch to the newdirection by encoding the field “NEXT DIRECTION” in the PHY header. Ifno adequate direction is found, the device switches to another direction(e.g., direction r) that is orthogonal to direction 1 and listens to thenext superframe. This process may be repeated until an adequatedirection is found.

On-demand beamforming may be performed between two devices, or between aPNC and one device. In one aspect of the disclosure, on-demandbeamforming is conducted in the CTA allocated to the link between twodevices. When a device is communicating with multiple devices, the samemessaging protocol as the proactive beamforming messaging protocol isused. In this case, the CTA will play the role of the beacon periodduring the beamforming phase, and will be used for data communicationthereafter. In the case where only two devices are communicating, sincethe CTA is a direct link between them, it is possible to employ a morecollaborative and interactive on-demand beamforming messaging protocol.

In a Q-omni phase, a first device begins its first transmission with L1Q-omni packets followed by L1 corresponding Q-omni listening periods,such as illustrated in FIG. 11. The first device keeps repeating thissection until a second device returns a response. Each Q-omni trainingpacket contains the Q-omni training packet IE, such as shown in FIG.12A. An Q-omni training response packet IE is shown in FIG. 12B.

The second device, which is capable of L2 Q-omni directions, sets itsreception direction to one of the L2 directions and listens to device1's first L1 transmissions and stores L1 LQFs. Device 2 moves to a newdirection and listens to device 1's second period of L1 transmissions.This process may be repeated until an adequate LQF is found.Alternatively, device 2 may choose to listen using all L2 directions,and then find the best LQF. At the end of this phase, both devices knowthe best combination of Q-Omni directions to use for exchanging data.

Device 2 may use the Q-Omni training response packet IE to inform device1 of its Q-omni capabilities (i.e. L2, as well as its own best firstdirection and second direction that it will use for all messaging).Furthermore, device 2 may inform device 1 of the best first and seconddirections it discovered from the L1 direction. Device 1's best Q-omnidirection would be labeled 11, and device 2's best Q-omni-directionwould be labeled 12. Similarly, device 2 may inform device 1 of itsdirectional capability.

FIGS. 13A-13C relate to a directional phase of on-demand beamforming.The first device uses R cycles to perform beamforming. The R cycles mayoccur within one CTA, or may be distributed over M superframes. Eachcycle comprises K sub-cycles, where N and K can change from one cycle toanother. This will allow for different search algorithms, such as randomand binary search. This also helps differentiate between acquisition andtracking. Each cycle is preceded by a Q-omni transmission outlining thestructure of the current cycle. Each sub-cycle includes N directionalpreambles followed by a Q-omni listening period. FIG. 13B shows an IEtransmitted in the Q-omni beacon, and the form of the response isillustrate in FIG. 13C.

Several aspects of a wireless network 1400 will now be presented withreference to FIG. 14, which is a network formed in a manner that iscompatible with the IEEE 802.15.3c Personal Area Networks (PAN) standardand herein referred to as a piconet. The network 1400 is a wireless adhoc data communication system that allows a number of independent datadevices such as a plurality of data devices (DEVs) 1420 to communicatewith each other. Networks with functionality similar to the network 1400are also referred to as a basic service set (BSS), or independent basicservice (IBSS) if the communication is between a pair of devices.

Each DEV of the plurality of DEVs 1420 is a device that implements a MACand PHY interface to the wireless medium of the network 1400. A devicewith functionality similar to the devices in the plurality of DEVs 1420may be referred to as an access terminal, a user terminal, a mobilestation, a subscriber station, a station, a wireless device, a terminal,a node, or some other suitable terminology. The various conceptsdescribed throughout this disclosure are intended to apply to allsuitable wireless nodes regardless of their specific nomenclature.

Under IEEE 802.15.3c, one DEV will assume the role of a coordinator ofthe piconet. This coordinating DEV is referred to as a PicoNetCoordinator (PNC) and is illustrated in FIG. 14 as a PNC 1410. Thus, thePNC includes the same device functionality of the plurality of otherdevices, but provides coordination for the network. For example, the PNC1410 provides services such as basic timing for the network 1400 using abeacon; and management of any Quality of Service (QoS) requirements,power-save modes, and network access control. A device with similarfunctionality as described for the PNC 1410 in other systems may bereferred to as an access point, a base station, a base transceiverstation, a station, a terminal, a node, an access terminal acting as anaccess point, or some other suitable terminology. The PNC 1410coordinates the communication between the various devices in the network1400 using a structure referred as a superframe. Each superframe isbounded based on time by beacon periods.

The PNC 1410 may also be coupled to a system controller 1430 tocommunicate with other networks or other PNCs.

FIG. 15 illustrates a preamble generation apparatus 1500 that may beused with various aspects of the disclosure, the preamble generationapparatus 1500 including an extended Golay code selection module 1502for obtaining an extended Golay code selected from a set of extendedGolay codes; an extended Golay code modification module 1504 thatmodifies the extended Golay code from the extended Golay code selectionmodule 1502; and a preamble generator 1506 that generates a preambleusing the modified extended Golay code from the extended Golay codemodification module 1504. A preamble transmitter 1508 then transmits thepreamble.

FIG. 16 illustrates a quasi-omni packet and directional preambletransmitter apparatus 1600 that may be used with various aspects of thedisclosure, the quasi-omni packet and directional preamble transmitterapparatus 1600 including a quasi-omni packet transmitter module 1602that transmits a plurality of quasi-omni packets, each quasi-omni packetbeing transmitted in a particular quasi-omni pattern; and, a directionalpreamble transmitter module 1604 that transmits a plurality of preamblesfrom the first device, each preamble being transmitted in one of aplurality of directional patterns.

FIG. 17 illustrates a beamforming feedback apparatus 1700 that may beused with various aspects of the disclosure, the beamforming feedbackapparatus 1700 including a quasi-omni packet detection module 1702 thatdetects a quasi-omni packet of a plurality of quasi-omni packetstransmitted in plurality of quasi-omni patterns from a first device; apreamble detection module 1704 that detects a preamble transmitted in adirectional pattern from the first device; a preferred patterndetermination module 1706 that determines a preferred pattern includingat least one of a quasi-omni pattern and a directional pattern; and afeedback transmitter module 1708 that transmits a feedback to the firstdevice including the preferred pattern.

Various aspects described herein may be implemented as a method,apparatus, or article of manufacture using standard programming and/orengineering techniques. The term “article of manufacture” as used hereinis intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media may include, but are not limited to, magnetic storagedevices, optical disks, digital versatile disk, smart cards, and flashmemory devices.

The disclosure is not intended to be limited to the preferred aspects.Furthermore, those skilled in the art should recognize that the methodand apparatus aspects described herein may be implemented in a varietyof ways, including implementations in hardware, software, firmware, orvarious combinations thereof. Examples of such hardware may includeASICs, Field Programmable Gate Arrays, general-purpose processors, DSPs,and/or other circuitry. Software and/or firmware implementations of thedisclosure may be implemented via any combination of programminglanguages, including Java, C, C++, Matlab™, Verilog, VHDL, and/orprocessor specific machine and assembly languages.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (“IC”), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The method and system aspects described herein merely illustrateparticular aspects of the disclosure. It should be appreciated thatthose skilled in the art will be able to devise various arrangements,which, although not explicitly described or shown herein, embody theprinciples of the disclosure and are included within its scope.Furthermore, all examples and conditional language recited herein areintended to be only for pedagogical purposes to aid the reader inunderstanding the principles of the disclosure. This disclosure and itsassociated references are to be construed as being without limitation tosuch specifically recited examples and conditions. Moreover, allstatements herein reciting principles, aspects, and aspects of thedisclosure, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

It should be appreciated by those skilled in the art that the blockdiagrams herein represent conceptual views of illustrative circuitry,algorithms, and functional steps embodying principles of the disclosure.Similarly, it should be appreciated that any flow charts, flow diagrams,signal diagrams, system diagrams, codes, and the like represent variousprocesses that may be substantially represented in computer-readablemedium and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown.

1. A method of communication, comprising: obtaining an extended Golaycode selected from a set of extended Golay codes; modifying the extendedGolay code; generating a preamble using the modified extended Golaycode; and transmitting the preamble.
 2. The method of claim 1, furthercomprising generating the set of extended Golay codes based on a Golaycode and a set of short sequences.
 3. The method of claim 2, whereineach of the short sequences comprises at least one of a row of a FourierTransform matrix and a Hadamard matrix.
 4. The method of claim 3,wherein the Fourier Transform matrix or the Hadamard matrix has fourrows and four columns.
 5. The method of claim 2, wherein the extendedGolay codes are generated by performing a Kronecker product of the Golaycode and one of the set of short sequences.
 6. The method of claim 2,wherein each of the short sequences comprises an inverse FourierTransform of a Kronecker sequence.
 7. The method of claim 2, wherein oneof the set of short sequences comprises a sequence selected from a groupconsisting of: [1 1 1 1]; [1 j −1 −j]; [1 −1 1 −1]; and [1 −j −1 j]. 8.The method of claim 1, wherein the set of extended Golay codes comprisesGolay codes with zero periodic cross-correlation.
 9. The method of claim1, where the modification comprises cyclically filtering the extendedGolay code with a time domain filter having a defined spectral mask. 10.The method of claim 1, where the modification comprises: performing aFast Fourier Transform (FFT) on the extended Golay code to create a setof subcarriers; attenuating at least one subcarrier of the set ofsubcarriers; and performing an inverse FFT of the attenuated at leastone subcarrier.
 11. The method of claim 10, wherein the attenuationcomprises zeroing out the at least one subcarrier of the set ofsubcarriers.
 12. A communication apparatus, comprising: means forobtaining an extended Golay code selected from a set of extended Golaycodes; means for modifying the extended Golay code; means for generatinga preamble using the modified extended Golay code; and means fortransmitting the preamble.
 13. The communication apparatus of claim 12,further comprising means for generating the set of extended Golay codesbased on a Golay code and a set of short sequences.
 14. Thecommunication apparatus of claim 11, wherein each of the short sequencescomprises at least one of a row of a Fourier Transform matrix and aHadamard matrix.
 15. The communication apparatus of claim 14, whereinthe Fourier Transform matrix or the Hadamard matrix has four rows andfour columns.
 16. The communication apparatus of claim 11, wherein theextended Golay codes are generated by performing a Kronecker product ofthe Golay code and one of the set of short sequences.
 17. Thecommunication apparatus of claim 11, wherein each of the short sequencescomprises an inverse Fourier Transform of a Kronecker sequence.
 18. Thecommunication apparatus of claim 11, wherein one of the set of shortsequences comprises a sequence selected from a group consisting of: [1 11 1]; [1 j −1 −j]; [1 −1 1 −1]; or [1 −j −1 j].
 19. The communicationapparatus of claim 12, wherein the set of extended Golay codes comprisesGolay codes with zero periodic cross-correlation.
 20. The communicationapparatus of claim 12, where the modification means comprises means forcyclically filtering the extended Golay code with a time domain filterhaving a defined spectral mask.
 21. The communication apparatus of claim12, where the modification means comprises: means for performing a FastFourier Transform (FFT) on the extended Golay code to create a set ofsubcarriers; means for attenuating at least one subcarrier of the set ofsubcarriers; and means for performing an inverse FFT of the attenuatedat least one subcarrier.
 22. The communication apparatus of claim 21,wherein the attenuation means comprises means for zeroing out the atleast one subcarrier of the set of subcarriers.
 23. A communicationapparatus, comprising: a processing system configured to: obtain anextended Golay code selected from a set of extended Golay codes; modifythe extended Golay code; generate a preamble using the modified extendedGolay code; and transmit the preamble.
 24. The communication apparatusof claim 12, wherein the processing system is further configured togenerate the set of extended Golay codes based on a Golay code and a setof short sequences.
 25. The communication apparatus of claim 11, whereineach of the short sequences comprises at least one of a row of a FourierTransform matrix and a Hadamard matrix.
 26. The communication apparatusof claim 14, wherein the Fourier Transform matrix or the Hadamard matrixhas four rows and four columns.
 27. The communication apparatus of claim11, wherein the extended Golay codes are generated by performing aKronecker product of the Golay code and one of the set of shortsequences.
 28. The communication apparatus of claim 11, wherein each ofthe short sequences comprises an inverse Fourier Transform of aKronecker sequence.
 29. The communication apparatus of claim 11, whereinone of the set of short sequences comprises a sequence selected from agroup consisting of: [1 1 1 1]; [1 j −1 −j]; [1 −1 1 −1]; or [1 −j −1j].
 30. The communication apparatus of claim 12, wherein the set ofextended Golay codes comprises Golay codes with zero periodiccross-correlation.
 31. The communication apparatus of claim 12, whereinthe processing system is further configured to cyclically filter theextended Golay code with a time domain filter having a defined spectralmask.
 32. The communication apparatus of claim 12, wherein theprocessing system is further configured to: perform a Fast FourierTransform (FFT) on the extended Golay code to create a set ofsubcarriers; attenuate at least one subcarrier of the set ofsubcarriers; and perform an inverse FFT of the attenuated at least onesubcarrier.
 33. The communication apparatus of claim 21, wherein theprocessing system is further configured to zero out the at least onesubcarrier of the set of subcarriers.
 34. A computer-program product forwireless communications comprising: a machine-readable medium encodedwith instructions executable to: obtain an extended Golay code selectedfrom a set of extended Golay codes; modify the extended Golay code;generate a preamble using the modified extended Golay code; and transmitthe preamble.
 35. A piconet coordinator comprising: an antenna; and aprocessing system configured to: obtain an extended Golay code selectedfrom a set of extended Golay codes; modify the extended Golay code;generate a preamble using the modified extended Golay code; and transmitthe preamble via the antenna.